1. Field of the Invention
This invention relates to a ribbon cartridge for a printer such as, for example, a thermal printer particularly adapted to be connected with an electronic computer for printing out the output thereof.
2. Description of the Prior Art
In general, many ink ribbon cartridges (referred to as ribbon cartridges hereinafter) for thermal-transfer serial printers of the line-sequential type and the ribbon-feeding mechanisms for such ribbon cartridges basically resemble compact audio tape cartridges and tape-feeding mechanisms for such audio cartridges, respectively. Specifically, such a ribbon-feeding mechanism includes a capstan and a pinch roller for feeding a ribbon at a constant speed or quantity, a friction clutch mechanism mounted on a shaft for a winding spool for transmitting a constant winding torque from a drive source to the winding spool shaft at all times so that the quantity of the ribbon wound around the shaft is adjusted at a constant level irrespective of the changing effective diameter of the ribbon wound around the winding spool. However, the ribbon-feeding mechanism of this type is disadvantageous in that it is complicated in construction and expensive to produce.
In order to eliminate the above-mentioned disadvantages, a proposal has been made for the system illustrated in FIG. 5. In this Figure, the ribbon-feeding mechanism as illustrated includes a ribbon-feeding roller 1, a winding side 2A of a ribbon, a coiled torsion spring 3 adapted to place the winding side 2A of the ribbon into pressure engagement with the ribbon-feeding roller 1, a feeding side 4 of the ribbon, a printing portion 5 of the ribbon extending from the feeding side 4 to the winding side 2A, a ribbon cartridge casing 6 receiving therein the above-described component members except for the ribbon-feeding roller 1, a printing head 7, a ribbon guide 8, a platen 9, and a printing paper 10 wound around the platen 9. Besides the above component members, there are housed in the ribbon cartridge casing 6 a tension mechanism (not shown) for applying a tension of a constant value to the printing portion 5 of the ribbon, and a brake mechanism (not shown) for preventing unnecessary rotation of the feeding-side ribbon 4 so as to avoid wasteful ribbon feed.
With the above construction, the printing portion 5 of the ribbon is mounted on the printing head 7 and the ribbon guide 8 in the manner as shown in FIG. 5 so that when the printing head 7 is placed by a printing command into pressure engagement with the printing paper 10, the printing portion 5 of the ribbon is intermediate the head and paper. Thereafter, the printing head 7 and the ribbon guide 8 are moved from the left to the right in FIG. 5 with their relative positions remaining unchanged, whereby the ink on the printing portion 5 of the ribbon is transferred to the printing paper 10, thus printing letters thereon. Upon completion of printing on the paper 10, the movement of the printing head 7 and the ribbon guide 8 is stopped and the printing head 7 and the printing portion 5 of the ribbon are moved away from the the printing paper 10. Then, the printing paper 10 is fed at a predetermined amount by rotation of the platen 9 so as to bring up a new printing line.
Subsequently, the printing head 7 and the ribbon guide 8 are moved from the right to the left in FIG. 5 to return to their initial positions, and simultaneously with this return movement, the ribbon-feeding roller 1 is caused to rotate in the counterclockwise direction in FIG. 5 so that the winding side 2A of the ribbon, being placed in pressure engagement with the ribbon-feeding roller 1 under the action of the coiled torsion spring 3, is forced to rotate in the clockwise direction in FIG. 5 thereby to move the printing portion 5 of the ribbon from the right to the left in FIG. 5 for winding thereof. The printing head 7 and the ribbon guide 8 are returned to their next print-starting positions and stopped there. Simultaneously with this, the rotation of the ribbon-feeding roller 1 is also stopped and the printing operation on one line is thus completed. Thereafter, the above-described operations are repeated by means of a printing command, and the amount of the winding side 2A of the ribbon wound increases accordingly up to a fully-wound condition indicted by the dotted line 2B in FIG. 5.
In the above-described operations, the reciprocating movement of the printing head 7 and the winding of the ribbon can be effected by a single drive source such as, for example, a stepping motor, i.e. by the forward or reverse rotation of the motor. Specifically, during printing operation, the winding of the ribbon is interrupted under the action of a one-way clutch (not shown), and during the return stroke, the return of the printing head 7 and the winding of the ribbon can be concurrently effected. Of course, these operations may also be made by respective independent drive sources.
The thermal printing ribbon is a one-time ribbon and hence it is required that the above-described winding amount of the ribbon be greater than the returning amount of the printing head 7 so that a used portion of the ribbon is not placed in a printing portion again. In this connection, the above-mentioned conventional ribbon cartridge has a major feature in that such a requirement can be met by taking into account only the angle of rotation of the ribbon-feeding roller 1 irrespective of the diameter of the wound ribbon 2A.
In the conventional ribbon-feeding mechanism of the above kind, the ribbon-feeding roller 1 employed comprises a toothed roller which is formed of a metal disc about 0.2 to 0.5 mm thick and having saw teeth formed in its outer peripheral portion, as illustrated in FIG. 5. Otherwise, the ribbon-feeding roller 1 may comprise a shaft having a plurality of short pins implanted radially on its outer peripheral surface. In either case, productivity is low and the cost of manufacturing becomes high.
Further, when the ribbon cartridge is not in use or is not loaded in a printer, the winding side 2A of the ribbon 2A is displaced by the torsion spring 3 toward the position indicated by the dotted line 2C wherein the ribbon 2A abuts against the peripheral wall of the cartridge casing 6. For loading of the cartridge in a printer, the ribbon-feeding roller 1 is moved away from its operating position shown in FIG. 5 in a direction indicated by an arrow and then the ribbon cartridge is loaded in the printer from above, or the ribbon cartridge is slid laterally and set in place in the printer, or the winding side of the ribbon displaced to the dotted-line position 2C is first slid toward the full-line position 2A and then the ribbon cartridge is loaded in the printer from above. Accordingly, in either case, the cartridge loading operation is very cumbersome.
Further, in cases where the printing portion 5 of the ribbon is slack in the free or non-loaded state thereof, it is difficult to turn the winding-side ribbon 2A for removal of such slack since the ribbon 2C is placed in frictional contact with the peripheral wall of the cartridge casing 6 under the bias of the torsion spring 3. As a result, it is preferable to turn the feeding side 4 of the ribbon in the rewinding direction and to this end, provision is needed for a knob by means of which the ribbon 4 can be turned. If, however, the printing portion 5 of the ribbon is damaged, rewinding of the feeding side 4 of the ribbon can not remove or remedy such damage, thus resulting in printing troubles.
On the other hand, although almost all thermal printing ribbons now in general use are one-time ribbons, it is expected in the near future that a multiuse or extended use ribbon reusable ten times or so will be developed and reduced to practice. In such a multiuse ribbon, the winding amount of the ribbon need not be greater than the return stroke of the printing head 7, and the ratio of the ribbon-winding amount to the printing head return stroke can be determined in accordance with the number of usable times required. However, this results in a change in rotation angle of the ribbon-feeding roller 1 and it is impossible to economically use the above-described two kinds of ribbons with the same printer.
Thus, the conventional ribbon cartridge for a printer as described above involves various disadvantages. Namely, the ribbon-feeding roller is costly and less productive; loading of the ribbon cartridge in a printer is troublesome and inefficient; slack in the printing ribbon can not be readily removed or remedied; and the ribbon cartridge has no satisfactory application with an extended use ribbon for the reason discussed immediately above and because of ribbon-feeding rollers of the type shown in FIG. 5 having projections on their outer peripheries.